The present invention relates to an improved printed circuit board, and more particularly to a printed circuit board for a capacitor keyboard.
FIG. 11 shows a sectional view of the structure of the conventional printed circuit board for a capacitor keyboard. A dielectric film substrate 31 is located on a base board 37, and lower and upper capacitor electrodes 32 and 33 are disposed on both surfaces of the dielectric film substrate 31 at a desired position. Thus, the lower and upper capacitor electrodes 32 and 33 and the dielectric film substrate 31 form a capacitor CA having a desired capacitance. A spacer 34 having an aperture 34A is located on the dielectric film substrate 31 in such a manner that the aperture 34A is opposed to the upper capacitor electrode 33. A movable film 35 having a contact 36 is located on the spacer 34 in such a manner that the contact 36 is opposed in spaced relationship to the upper capacitor electrode 33 through the aperture 34A of the spacer 34. When the movable film 35 at the position of the contact 36 is depressed, the contact 36 is brought into contact with the upper electrode 33 to allow a charge in the capacitor CA to be discharged.
Such a capacitor keyboard switch having a dielectric film substrate, capacitor electrodes formed on both surfaces of the dielectric film substrate, and a switching movable electrode arranged in opposed relationship to the capacitor electrodes is disclosed in Japanese Patent Laid-Open Publication No. 60-117512, and U.S. Pat. Nos. 4,659,879 and 3,951,250, for example.
As described above, the conventional capacitor keyboard has a structure such that the lower electrode 32 and the upper electrode 33 are formed on both surfaces of the dielectric film substrate 31, and the contact 36 of the movable film 35 is opposed in spaced relationship to the upper electrode 33 through the aperture 34A of the spacer 34, so as to be made contactable with the upper electrode 33. However, it is necessary to make a pitch between the adjacent switches coincident with a dimension defined by the International Standard of a keyboard (ISO Standard). Accordingly, the mounting position of the capacitor electrode pairs 32 and 33 is limited, and the distance therebetween is resultantly fixed. As a result, lead patterns formed to pass between the adjacent capacitor electrode pairs are closely arranged, causing the generation of cross talk or noise trouble.